(562an) The Synergistic Emulsification of Cactus Mucilage with d-Limonene and Silica Nanoparticles for Oil in Water Emulsion

Authors: 
Guo, F., University of South Florida
Veisi, Z., University of South Florida
Alcantar, N., University of South Florida
It is common knowledge that crude oil does not dissolve easily in water. Therefore, crude oil floats on the ocean surface and hardly dissolve after an oil spill. Spilled oil can produce extensive damage to marine and wildlife habitats and tourism industries. As a rapid response method, dispersants can remove spilled oil from the sea surface and disperse it as tiny oil/dispersant/water droplets. However, the application of extremely high amounts of chemical dispersants could be detrimental to marine life and the costal environment. In this research, we are proposing to use a natural surfactant from cactus plant to stimulate the dispersion process of oil in water (O/W). This natural dispersant is extracted from the Opuntia ficus indica cactus plant. Compared with the traditional chemical dispersants, cactus mucilage extract has the advantages of being biodegradable, non-toxic, and can be obtained through sustainable agriculture. The cactus plant-based mucilage can diffuse to the interface when applied to O/W emulsion. Then, tiny oil droplets are surrounded by surfactants and dissolved into water. By the mixing action of the waves, spilled oil and water can be combined in two ways: natural dispersion and water-in-oil emulsification. Cactus mucilage extract can push the balance between natural dispersion and water-in-oil emulsification strongly towards natural dispersion. This dispersion process can improve the opportunity for biodegradation of the spilled oil by increasing the contact area between water and oil. The properties of cactus mucilage extract as a dispersant were studied on the surface tension, droplet size and stability of O/W emulsions, toxicity, and dispersion effectiveness. Synthetic seawater and the surrogate oil from British Petroleum (properties similar to the Macondo rig) were used. The synergistic emulsification mechanism among the surfactant, organic solvent, and silica nanoparticles have been studied. A food grade solvent, d-limonene, and silica nanoparticles have been applied with the cactus mucilage extract to improve its dispersion ability. It is found that the O/W emulsion had a lower surface tension due to the application of the solvent, which can push the balance strongly from O/W emulsion towards dispersion. Furthermore, adding silica nanoparticles increased the stability of the O/W emulsion. Baffled flask test was used to quantify to dispersion effectiveness. The factors and the levels of each factor were as follows: DOR (mg/mg) (control, 1:200, 1:100, 1:75, 1:50; 1:35, 1:20, and 1:10). The baffled flask test showed that with the synergy of both d-limonene and silica nanoparticles, the dispersion effectiveness of the cactus mucilage has been significantly improved. The ratio of cactus mucilage extract/d-limonene/SiO2 has also been optimized through baffled flask test. The average droplets size of O/W emulsion was smaller in the systems with cactus mucilage extract/d-limonene/SiO2 when compared with the systems using the conventional dispersant COREXIT EC9500A by measuring with optical microscope. The smaller droplets size implies that cactus mucilage extract/d-limonene/SiO2 would provide a better stability to O/W emulsion.